The present invention is an improvement over the NAVIGATION SYSTEM USING RE-TRANSMITTED GPS disclosed in the U.S. patent application Ser. No. 08/127,039, filed Sep. 24, 1993, the entire disclosure of which is expressly incorporated by reference in the present patent application.
1. Field of the Invention
The present invention relates generally to a retransmitted Global Positioning System (GPS) interferometric system, and more particularly pertains to a retransmitted GPS interferometric system using retransmission of GPS signal in combination with an interferometer for determining the angular deviations of an aircraft relative to a landing site in both vertical and horizontal planes, by using the accumulated phase of the GPS carrier signal.
2. Discussion of the Prior Art
Both the FAA and the Navy are actively pursuing a navigational capability for approach and landing of aircraft of all types including fixed wing, STOL, VSTOL and helicopter aircraft. Several key objectives include a navigational capability for precision landing and ultimately to provide for a fully automatic hands-off landing (autoland), which is generally accomplished by an aircraft based navigation system and autopilot. A flare maneuver, touchdown and rollout completes the landing for the land based case. Navigation is required by the aircraft in all of the landing phases. For a naval carrier landing, it is the carrier which determines the position of the aircraft (relative to the carrier deck), and determines the commands for the aircraft autopilot.
Precision landing has been divided into three categories, each requiring progressively greater accuracy as the type of landing selected ranges from manual to automatic. The decision heights and navigational accuracy requirements for each category is given in Table 1.
TABLE 1 ______________________________________ Precision Approach/Landing Requirements accuracy req. ht. abv surface lateral vertical Category (ft) (ft-2.sigma.) (ft-2.sigma.) ______________________________________ I 200 +56.1 +13.6 II 100 +16.9 +5.7 III 50* +13.2* +1.8* ______________________________________ *runway threshold values
Whereas fixed wing aircraft generally use a low angle landing approach (usually 3 deg), the other types require a high angle approach, and therefore the landing navigation system must be flexible enough to provide for all types of approaches and landings. Further, the navigational capability must be provided in all phases of the landing so that the aircraft can know its position with respect to both the runway approach threshold and the runway end (for rollout, waveoff or runway exit).